In the related art, cleaning of substrates such as semiconductor wafers is achieved by immersing an object to be cleaned in a cleaning bath having cleaning liquid stored therein and oscillating an ultrasonic transducer provided on a bottom of the cleaning bath. Since large-sized objects to be cleaned cannot be immersed in the cleaning bath, a handy-type ultrasonic cleaning tool is used for such objects to be cleaned. The handy-type ultrasonic cleaning tool is used for preventing re-adherence of particle, for example, for semiconductor wafer substrates, depending on characteristics and materials of objects to be cleaned.
Disc-shaped substrates such as semiconductor wafer substrates and glass substrates need cleaning after processes such as polishing and etching. Cleaning of a substrate such as a semiconductor wafer is performed to remove particle adhered to an edge face of the substrate due to polishing. This is for chucking the edge faces of the substrates at the time of handling the substrates or for preventing the edge faces of the substrates from being contaminated by particle adhered to the edge faces of the substrates at the time of storage of the substrates into a cassette.
Patent Literature 1 discloses a method of cleaning a glass substrate including rotating a disc-shaped glass substrate with a main surface thereof extending perpendicularly and flowing cleaning liquid W irradiated with an ultrasonic wave on an outer peripheral edge face of the rotating glass substrate. According to FIG. 1 and FIG. 2 in Patent Literature 1, the cleaning liquid W irradiated with the ultrasonic wave is flowed in a perpendicular direction on outer peripheral edge faces of a plurality of glass substrates held perpendicularly at a distance from each other in parallel in a vertical direction. In other words, the cleaning liquid W is flowed from the outside of the outer peripheral edge faces of the glass substrates toward centers of the glass substrates to clean the outer peripheral edge faces of the glass substrates.